To find the velocity given the kinetic energy (KE) and mass (m), we can use the formula for kinetic energy:
\[ KE = \frac{1}{2} m v^2 \]
Where:
- \( KE \) is the kinetic energy (18 J)
- \( m \) is the mass (0.0004 kg)
- \( v \) is the velocity
We can rearrange the formula to solve for velocity \( v \):
\[ v = \sqrt{\frac{2 \cdot KE}{m}} \]
Now, substitute the values into the equation:
- Calculate \( 2 \cdot KE \):
\[ 2 \cdot 18 , \text{J} = 36 , \text{J} \]
- Divide by the mass:
\[ \frac{36 , \text{J}}{0.0004 , \text{kg}} = 90000 , \text{m}^2/\text{s}^2 \]
- Take the square root:
\[ v = \sqrt{90000} \approx 300 , \text{m/s} \]
Thus, the velocity is approximately 300 m/s.
The correct answer from the options given is 300 m/s.